This invention relates to compounds and compositions comprising specific metal salts of hexahydrophthalic acid (hereinafter HHPA) in order to provide highly desirable properties within thermoplastic articles. The inventive HHPA derivatives are useful as nucleating and/or clarifying agents for such thermoplastics, and are practical to produce and handle. Such compounds provide excellent crystallization temperatures, stiffness, and acid scavenger compatibility within target polyolefins. Also, such compounds exhibit very low hygroscopicity and therefore excellent shelf stability as powdered or granular formulations. Thermoplastic additive compositions and methods of producing polymers with such compounds are also contemplated within this invention.
All U.S. patents cited below are herein fully incorporated by reference.
As used herein, the term xe2x80x9cthermoplasticxe2x80x9d is intended to mean a polymeric material that will melt upon exposure to sufficient heat but will retain its solidified state, but not prior shape without use of a mold or like article, upon sufficient cooling. Specifically, as well, such a term is intended solely to encompass polymers meeting such a broad definition that also exhibit either crystalline or semi-crystalline morphology upon cooling after melt-formation. Particular types of polymers contemplated within such a definition include, without limitation, polyolefins (such as polyethylene, polypropylene, polybutylene, and any combination thereof), polyamides (such as nylon), polyurethanes, polyesters (such as polyethylene terephthalate), and the like (as well as any combinations thereof).
Thermoplastics have been utilized in a variety of end-use applications, including storage containers, medical devices, food packages, plastic tubes and pipes, shelving units, and the like. Such base compositions, however, must exhibit certain physical characteristics in order to permit widespread use. Specifically within polyolefins, for example, uniformity in arrangement of crystals upon crystallization is a necessity to provide an effective, durable, and versatile polyolefin article. In order to achieve such desirable physical properties, it has been known that certain compounds and compositions provide nucleation sites for polyolefin crystal growth during molding or fabrication. Generally, compositions containing such nucleating compounds crystallize at a much faster rate than unnucleated polyolefin. Such crystallization at higher temperatures results in reduced fabrication cycle times and a variety of improvements in physical properties, such as, as one example, stiffness.
Such compounds and compositions that provide faster and/or higher polymer crystallization temperatures are thus popularly known as nucleators. Such compounds are, as their name suggests, utilized to provide nucleation sites for crystal growth during cooling of a thermoplastic molten formulation. Generally, the presence of such nucleation sites results in a larger number of smaller crystals. As a result of the smaller crystals formed therein, clarification of the target thermoplastic may also be achieved, although excellent clarity is not always a result. The more uniform, and preferably smaller, the crystal size, the less light is scattered. In such a manner, the clarity of the thermoplastic article itself can be improved. Thus, thermoplastic nucleator compounds are very important to the thermoplastic industry in order to provide enhanced clarity, physical properties and/or faster processing.
As an example, dibenzylidene sorbitol derivatives are common nucleator compounds, particularly for polypropylene end-products. Compounds such as 1,3-O-2,4-bis(3,4-dimethylbenzylidene) sorbitol (hereinafter DMDBS), available from Milliken Chemical under the trade name Millad(copyright) 3988, provide excellent nucleation and clarification characteristics for target polypropylenes and other polyolefins. Other well known nucleator compounds include sodium benzoate, sodium 2,2xe2x80x2-methylene-bis-(4,6-di-tert-butylphenyl) phosphate (from Asahi Denka Kogyo K.K., known as NA-11), aluminum bis[2,2xe2x80x2-methylene-bis-(4,6-di-tert-butylphenyl)phosphate] (also from Asahi Denka Kogyo K.K., known as NA-21), talc, and the like. Such compounds all impart high polyolefin crystallization temperatures; however, each also exhibits its own drawback for large-scale industrial applications.
For example, of great interest is the compatibility of such compounds with different additives widely used within typical polyolefin (e.g., polypropylene, polyethylene, and the like) plastic articles. For instance, calcium stearate is a very popular acid neutralizer present within typical polypropylene formulations to protect the stabilizing additives (such as light stabilizers, antioxidants, etc.) from catalyst residue attack. Unfortunately, most of the nucleator compounds noted above also exhibit deleterious reactions with calcium stearate within polyolefin articles. For sodium, and other like metal ions, it appears that the calcium ion from the stearate transfers positions with the sodium ions of the nucleating agents, rendering the nucleating agents ineffective for their intended function. As a result, such compounds sometimes exhibit unwanted plate-out characteristics and overall reduced nucleation performance (as measured, for example, by a decrease in crystallization temperature during and after polyolefin processing). Other processing problems are evident with such compounds as well.
Other problems encountered with the standard nucleators noted above include inconsistent nucleation due to dispersion problems, resulting in stiffless and impact variation in the polyolefin article. Substantial uniformity in polyolefin production is highly desirable because it results in relatively uniform finished polyolefin articles. If the resultant article does not contain a well-dispersed nucleating agent, the entire article itself may suffer from a lack of rigidity and low impact strength.
Furthermore, storage stability of nucleator compounds and compositions is another potential problem with thermoplastic nucleators and thus is of enormous importance as well. Since nucleator compounds are generally provided in powder or granular form to the polyolefin manufacturer, and since uniform small particles of nucleating agents is imperative to provide the requisite uniform dispersion and performance, such compounds must remain as small particles through storage. Certain nucleators, such as sodium benzoate, exhibit high degrees of hygroscopicity such that the powders made therefrom hydrate easily resulting in particulate agglomeration. Such agglomerated particles may require further milling or other processing for deagglomeration in order to achieve the desired uniform dispersion within the target thermoplastic. Furthermore, such unwanted agglomeration due to hydration may also cause feeding and/or handling problems for the user.
These noticeable problems have thus created a long-felt need in the thermoplastic industry to provide nucleating/clarifying agents that do not exhibit the aforementioned problems and provide excellent peak crystallization temperatures for the target thermoplastics themselves, particularly with a wide variety of typical and necessary acid scavenger additives. To date, the best compounds for this purpose remain those noted above. Unfortunately, nucleators exhibiting exceptionally high peak crystallization temperatures, low hygroscopicity properties, excellent dispersion and concomitant clarity and stiffness, as well as compatibility with most standard polyolefin additives (such as, most importantly, calcium organic salt acid scavengers) have not been accorded the different thermoplastic industries. Such problems are not limited to polyolefins and are common within all thermoplastic applications in which nucleating agents are used.
Therefore, an object of the invention is to provide a nucleator compound and compositions thereof that exhibit excellent calcium stearate compatibility within target thermoplastic articles and formulations. A further object of the invention is to provide a thermoplastic nucleating agent that provides excellent high peak crystallization temperatures, for example, to polypropylene articles and formulations, and also exhibits extremely low hygroscopicity in order to accord an extremely good shelf-stable additive composition. Another object of the invention is to provide an easily dispersed nucleator compound such that said polyolefin exhibits very high stiffness and good clarity. Additionally, it is an object of this invention to provide a nucleator compound or composition which may be used in various thermoplastic media for myriad end-uses.
Accordingly, this invention encompasses metal salts of a compound conforming to Formula (I) 
wherein M1 and M2 are the same or different and are selected from at least one metal cation of calcium, strontium, lithium, and monobasic aluminum, and wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, and R10 are either the same or different and are individually selected from the group consisting of hydrogen, C1-C9 alkyl [wherein any two vicinal (neighboring) or geminal (same carbon) alkyl groups may be combined to form a carbocyclic ring of up to six carbon atoms], hydroxy, C1-C9 alkoxy, C1-C9 alkyleneoxy, amine, and C1-C9 alkylamine, halogens (fluorine, chlorine, bromine, and iodine), and phenyl. The term xe2x80x9cmonobasic aluminumxe2x80x9d is well known and is intended to encompass an aluminum hydroxide group as a single cation bonded with the two carboxylic acid moieties. Furthermore, form each of these potential salts, the stereochemistry at the asymmetric carbon atoms may be cis or trans, although cis is preferred.